A conventional network is expressed conceptually by the network model shown in FIG. 16. In FIG. 16, each terminal registers a terminal address (for example, a network address or a host address) as its identifier. Moreover, a send terminal sends an event (packet) comprising destination address (destination terminal address) and data onto the network. That is, the basic concept of a conventional information network is to deliver an event to its destination accurately based on a destination address.
A case is considered wherein recommendation services (personalized information recommendation services for recommending personalized information to each user, and yellow pages services such as search services and the like) are achieved with this network. Conventionally, intervention with a centralized server system (broker) is always necessary as shown in FIG. 18 in order to realize a personalized information recommendation service. Similarly, in a yellow pages service, it is also necessary to assume a broker called a search service. Such a centralized business model involving a broker is called the broker model. In this broker model, a broker takes the role of connecting an information provider and a user. That is, it is only possible for a user and an information provider to meet through a broker.
A detailed description of the broker model described above will be given using FIG. 19. As shown in FIG. 19, in a business model comprising three business roles, namely an end user (consumer 101 in the figure), an information provider (content provider 102), and additionally a service provider (content information provider) 103, the service provider 103 achieves a recommendation service for recommending content appropriate to an end user (consumer 101) by managing registered content information from an information provider (content provider 102) and registered end user preference information from an end user (consumer 101), and also comparing the registered content information and the end user preference information. Such a service provider corresponds to a broker.
Specific services include search services such as Yahoo and the like, trading services, and personalized information recommendation services for recommending content matching the interests of an end user without direct intervention by the end user.
Each such service is achieved as an integrated type service system (service application) in an individual service provider 103 on a network 109 or a content distribution network 110 as shown in FIG. 20.
This causes the following problems in the broker model.
(1) Since there is no mechanism for the information provider (content provider 102) to announce content information to the end user (consumer 101) without the intervention of a third party, it is not possible to achieve an information provider (content provider) initiative type, order-taking society, wherein the information provider (content provider 102) itself distributes content information. That is, the information provider (content provider 102), being a content provider, cannot distribute content information under its own policy without the intervention of a third party.
(2) In order to obtain a recommendation service from the service provider 103, the end user (consumer 101) must explicitly recognize the existence, the location, and the access method of the service provider 103.
(3) It is not possible to share content, content information and end user preference information among different service providers 103 easily. Heretofore, information has been shared by exchanging information according to protocols agreed in advance among service providers 103.
(4) Because of centralized management of content information and end user preference information by the service provider 103, it is not easy to build a system with high scalability. Heretofore, a classic method such as preparing a plurality of server systems for managing content information and end user preference information, or the like, has been used.
Incidentally, distributed processing technology such as the WWW (World Wide Web), CORBA and the like, provides an environment where content distributed onto heterogeneous distributed systems can be easily obtained, and also makes it possible for anybody to become a content provider easily. On the other hand, it is not easy to find content required by an end user among the vast amount of content flooding the world, and so the early establishment of techniques to realize such is desirable.
Taking such situations and the above-described problems into consideration, a brokerless model is proposed in which an information provider (content provider) can provide appropriate content directly to an appropriate end user without assuming the existence of a broker.
For methods of realizing a brokerless model, there are Gnutella, an invention by Sun (U.S. Pat. No. 5,870,605: Reference 1), and an invention by NEC (Japanese Patent Application No. 11-328654: Reference 2).
Gnutella is a network for searching and discovering a specific entity from among an unspecified number of entities (information) distributed around the Internet based on a P2P (Peer-to-Peer) interaction model. Here, in Gnutella, an entity is also called a servent. That is, each information provider performs massively distributed management of metadata (meta files), and establishes arbitrary connections between meta files (between hosts in which meta files are stored), and thus an massively distributed database of metadata is built by only the information provider. Then, collaboration of information providers with each other enables the construction of a distributed search network of metadata that does not require a broker. However, search request packets from consumers are broadcast to all information providers based on the connection. That is, since P2P type interactions are repeated to all hosts based on the connection information, unnecessary traffic increases in proportion to an increase in the number of hosts and metadata categories, so there is a problem of an extreme drop in scalability. Furthermore, there is a problem not only in scalability but also in aspects of interoperability, information sharing, extendibility, security, privacy, and the like.
Reference 1 describes a method that enables the request and use of information in a situation where an information provider (Publisher) and a user (Subscriber) have no knowledge of each other, without a broker. However, since it does not have a routing mechanism that suppresses unnecessary event forwarding, there is a problem of scalability. Furthermore, since it does not have an ontology (mechanism for converting event dictionaries) between territories, there are also problems in aspects such as interoperability, information sharing, extendibility, and the like. That is, reference 1 defines a territory where a common event dictionary (event dictionary) is shared. However, the method of realizing a territory and the method of sharing information among different territories are not made clear. Therefore regarding territory, the description of specific implementations is poor.
Reference 2 proposes information routing capable of routing not only packets having specific destination addresses but also packets containing only an assignment of region of interest. Searching that does not require a broker can be achieved by information routing. However, it does not have the concepts of an event place, which guarantees a unique ontology system and limits the event delivery range, gateway and session. As a result, there are problems in aspects of scalability, security, privacy, interoperability, information sharing, extendibility, and the like.
Accordingly, realization techniques of conventional brokerless models have the following four main problems.
Lack of Protection of Security and Privacy
There is no mechanism for limiting the information delivery range. That is, the spread of an event cannot be limited. As a result, it is possible for anybody who is connected to a network to see information.
Furthermore, the endpoint of information is a terminal of an end user, and this is accessible from the outside. Therefore, even if information that is not wanted to be opened outside is placed on the terminal, there is a possibility of releasing the information if it is connected to a network.
Since there is no session concept, although a network can be constructed by only event send and receive terminals, it is not possible to separate a network provider and an event sender-receiver.
Lack of Interoperability
In the case where regions with different semantic information systems (ontology systems) are created, since it does not have a mechanism for connecting those regions, it is not possible to share events among them.
It is not possible to forward only those events that are necessary.
Lack of Extendibility
It is difficult to dynamically add and delete functions.
It is not easy to expand network scale.
Lack of Scalability
Increases in number of event sender-receivers cannot be handled.
Increases in semantic information categories (metadata categories) cannot be handled.
Forwarding of unnecessary events cannot be suppressed.